Non-volatile memory devices (ROM, PROM, EPROM, EEPROM, etc) are widely known. Also they have been widely used in applications where the data needs to be protected, like in home applications, mobile applications, and set-top boxes (pay TV, satellite TV, etc). In the last decades various methods of attacking data on non-volatile memory devices have been developed:                front-side de-processing combined with optical imaging        back-side de-processing combined with voltage contrast imaging        microprobing        UV treatment        Software attack        FIB (cut and sense),        etc.        
In general non-volatile memories like floating gate-based memories and ONO-based memories have been regarded as very secure to these attacks. However, recently, in C. De Nardi et al., Microelectronics Reliability, Vol. 45 (2005), p 1514-1519, a method has been published which enables retrieval of data from EEPROM memory devices. This publication discloses a method to measure “on site” programmed charges in EEPROM devices. Electrical AFM based techniques (Electric Force Microscopy (EFM) and Scanning Kelvin Probe Microscopy (SKPM) are used to probe directly floating gate potentials. Both preparation and probing methods are discussed. Sample preparation to access floating gate/oxide interfaces at a few nanometers from the back-side without discharging the data reveals to be the key point, more than the probing technique itself. This method will also be referred to as back-side voltage contrast imaging.
So, a drawback of the known non-volatile memory devices is that data stored thereon may no longer be secure enough to external attacks.